Re: PE and LE

Hi

Physical extents fill up the physical volume - default 4 MBLogical extents fill up the logical volume - Default 4 MBAn LE is written into ramA PE is written onto the pvWhen the LE is 'flushed' out of RAM the PE is written to diskBoth extents are filled with file system blocks of data - default size 1024 bytes.You can fill a 4MB extent with 4096 blocks of data.

Re: PE and LE

There are no free PEs, so you cannot create another LV.

Hope this helps!RegardsTorsten.

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Re: PE and LE

This means:* You can add up to 15 more disks/storage LUNs to this VG. (Max PV - Cur PV = 15)Because you are now using only 1 disk, there is plenty of room for growth in this aspect.

* Each of those disks should be 32512 MeB or less in size; if you try to add a larger disk to this VG, only the first 32512 MeB is actually used. (PE size * Max PE per PV = 32512 MeB)As a single physical disk can today hold one terabyte or more, this is very likely going to be a bottleneck.

* With vgmodify, you can increase the Max PE per PV value up to 65535; this would allow adding disks of 2097120 MeB (= slightly less than 2 TeB) to this VG, increasing the maximum size of the VG to 33553920 MeB = about 31 TeB.

* With vgmodify, you can also increase the Max PV value to 255; if you use vgmodify to change both values, the absolute maximum size is 509 TeB (which is way larger than currently supported by any filesystem).

When a LVM 1.0 VG is created, the system administrator must estimate how big the VG will grow in the future, and adjust the "PE size", "Max PE per PV" and "Max PV" values accordingly.

With vgmodify, you can change the "Max PE per PV" and "Max PV" values later; however, the PE size is set in stone at VG creation time and cannot be changed without destroying & recreating the VG.

It's usually easier to manage a few large disks than a large number of small disks. And if I can choose between a large PE size or a large "Max PE per PV", I would prefer larger PE size. Less PEs = smaller LVM metadata = smaller LVM configuration backup files in /etc/lvmconf on the root filesystem. (With large "Max PE per PV" and "Max PV", those files can become inconveniently large.)

The _minimum_ useful size of a LV is always one extent, so if you increase the PE size, the minimum size of a LV increases; but if you have a multi-terabyte VG, there is usually no need to micro-manage each megabyte individually.